A new NIST SEM magnification calibration standard has been fabricated and characterized in production prototype form. The SRM 2090A samples contain structures ranging in pitch from 3000 micrometers to 0.2 micrometers and are useful at both high and low accelerating voltages. The design and fabrication of the samples has incorporated many of the improvements suggested through two previous prototype series. Since the low- accelerating voltage, critical-dimension measurement scanning electron microscope has assumed an important role in modern semiconductor process control. We investigate the use and performance of the samples in a representative instrument. Scan area contamination from a prolonged high magnification scan is shown to be a significant issue. A cleaning procedure developed for a previous prototype series has been modified to obtain acceptable results on the present samples.